1. Field of the Invention
Citrate esters are useful as plasticizers for polyvinyl chloride (PVC) resins as certain of these esters provide a low order of toxicity when compared to phthalate esters which have been conventionally used. Other advantages have been noted using certain citrate esters as plasticizers in PVC compositions and articles, including improved resistance to soapy water extraction and low temperature and transport properties.
The preparation of the citrate esters has been found to be significantly enhanced by the utilization of certain organic titanate catalysts which allow the excess alcohol to be removed after the esterification step.
2. Description of the Prior Art and Objectives of the Invention
Citrate esters commercially produced using citric acid have long been available and have been used as plasticizers for PVC resins. However, the performance of articles produced from the PVC resin compositions whether utilizing citrate esters known to date or conventional phthalate plasticizers have had many inherent disadvantages. For example, medical-grade PVC compositions are used to form blood bags, tubing and a variety of health-related articles and in recent years toxicity has been a major concern for manufactures of such articles. Recent reports have identified di-2-ethylhexyl phthalate (DEHP) or (DOP) and di-2-ethyl-hexyl adipate (DEHA) as hepatocarcinogens in rodents. While certain of the phthalates have excellent plasticizing qualities, their suspected carcinogenic nature renders them doubtful candidates for future medical-grade uses. As an alternative, known citric acid esters such as acetyltri-n-butyl and tri-n-butyl citrate were tried as PVC plasticizers in medical-grade applications but it was determined that these compounds were not entirely satisfactory due to their high soapy water extraction percentages and would therefore not be useful in many medical area applications. Also, it has been found that new production techniques had to be devised for the newer citric acid esters which were determined to have suitable toxicity and physical characteristics when used as PVC plasticizers.
It is therefore an objective of the present invention to provide PVC plasticizers which provide superior toxicity test results in biological studies.
It is also an objective of the present invention to provide plasticizers for PVC compositions which can be processed without difficulty using conventional extrusion, calendering, or plastisol techniques.
It is yet another objective of the present invention to provide new citric acid esters namely: acetyltri-n-hexyl citrate, n-butyryltri-n-hexyl citrate, acetyltri-n-(hexyl/octyl/decyl)citrate, and acetyltri-n-(octyl/decyl)citrate which can be used as plasticizers having desirable physical characteristics when imparted into PVC compositions.
It is still another objective of the present invention to provide PVC compositions and formed articles therefrom having superior results in toxicology studies concerning dermal toxicity, oral toxicity and genetic assays.
It is also an objective of the present invention to provide a new process for the low temperature manufacture of the four new citric acid esters utilizing organic titanates to provide economical and efficient production methods. be demonstrated to those skilled in the art as set forth in detail below.